Over the weekend, that scenario happened. Not in America, but in the country where President Obama's father was born: Kenya. A glittering, up-market mall in the capital, Nairobi, has looked like a violent, blood-spattered Hollywood movie: heavily armed, well-trained gunmen dressed in black on a rampage; hostages; hundreds dead and injured; an utterly overwhelmed police force.

The same theme and grievances as 9/11 are woven through this horror. The gunmen are not from al-Qaeda; they are from a group known as al-Shabab in Somalia, the country that neighbors Kenya. But the groups are affiliated. They could almost be clones. Al-Shabab for years has ruled and terrorized much of Somalia, meting out such sharia law punishment as beheadings and stoning women to death for adultery, even if the women had been raped.

President Obama's most effective and dramatic move would be to go to Nairobi. He is half-Kenyan. He has the status of a near-God there. His influence is incalculable. He could say what needs to be said to Kenyans, to al-Shabab, to Americans and to the world: Kenyans need to stay strong and to keep forces in Somalia, not withdraw them as the attackers want; such attacks are painful and cowardly; the only way to fight them is by standing firm.

Somalia next Afghanistan?

Just as important: The fight is not just a Kenyan, or African, fight. Somalia could be the new Afghanistan. A lawless, fundamentalist Somalia could incubate a Somali Osama bin Laden and new attacks on the USA, just as Afghanistan protected and nurtured bin Laden and al-Qaeda.

For a decade and a half, the warning signs have been growing. Al-Qaeda blew up the U.S. Embassy in Nairobi in 1998. The truck bomb killed more than 200, and there was a simultaneous attack on the U.S. Embassy in neighboring Tanzania. An Israeli hotel on the tourist beaches of the Indian Ocean was attacked more than a decade ago.

I grew up in the region in the dying days of the colonial empire and already sensed back then the religious and tribal forces that could be unleashed. An imaginative future al-Shabab attack on the U.S. is even the premise of a novel I am finishing.

There is a catch to an Obama Kenya trip. A Catch-22.

Kenyan President Uhuru Kenyatta is accused of war crimes for allegedly inciting violence after elections in 2007, in which more than 1,000 people died. His trial at the International Criminal Court is set for November. An Obama trip could be seen as supporting Kenyatta, undermining the charges.

Benefits of Obama visit

The benefit, though, would outweigh this risk. Obama could focus attention on the charges, too, and underscore how volatile and difficult the whole region is, and how much the U.S. needs to focus on it. Kenya has long been considered an oasis of stability on a violent continent. Kenyatta is the son of the revered first post-colonial president, Jomo Kenyatta.

The Nairobi shopping mall attack is heartbreaking. The stories could so easily be American stories. A popular radio host killed where she had earlier posted photos onto her Instagram account. A respected, elderly poet and professor from Ghana was also gunned down. As the days go by, there will be more victims identified, more grief at lives ended too violently, too soon, as they were on 9/11.

The message of the attackers could easily be imagined in an attack, say, on the Mall of the America. The attackers even called for Muslims to run away. As on 9/11, they are attacking a modern, democratic way of life. After 9/11, the French newspaper Le Monde famously carried a headline: We Are All Americans.

After the Nairobi attack, the message should be "We Are All Kenyans." Not just in our sympathy. But also in going all out to prevent another terrorist attack.

Leaving Somalia to al-Shabab is not an option.

Author and journalist Louise Branson is a former USA TODAY editorial writer and London Sunday Times foreign correspondent. She is writing an international thriller.